1. Field of the Invention
This invention relates in general to a reflex transmitter for a bidirectional light waveguide communication systems and in particular to a novel communication system.
2. Description of the Prior Art
In bidirection communication systems formed from monomode light waveguides, it is possible to provide a light source or light sources at only one end of the light waveguide link and to provide reflection means as well as an optical modulator at the other end of the light waveguide link as is disclosed in U.S. Pat. No. 4,195,269 particularly at column 2, lines 32-44 and 51-55. See also German DE A No. 2 708 606. Also see Electronic Letters 22 1986, Vol. 9, Pages 479-481, Electronic Letters 8 May 1986, Vol. 22 No. 10, Page 517 and 518. Entwicklungstendenzen Der Integrierten Optik in Telecom Report 10 1987, Pages 90-98 by Franz Auracher et al, Optics Communication, Vol. 36, No. 4, 15 February 1981, Pages 281-284. U.S. Pat. No. 4,291,939, U.S. Pat. No. 4,436,365.
An optical intensity modulator can be formed with a controllable optical directional coupler as described in Telecom Report 10 (1987) to Pages 90-98 in FIGS. 8 and 9. Such an optical directional coupler includes two identical optical strip waveguides which are narrow thin strips formed in a substrate by injection of, for example, titanium into lithium niobate and the strips have a higher optical refractive index than the substrates. These strips are spaced in close proximity at a distance of typically 5 um from each other over a defined length so that the optical fields of waves guided in the strip waveguides overlap and periodically repeated with what is referred to as the coupling length light energy is coupled from one to the other strip waveguides. Electrodes are provided between and next to the strip waveguides and an electrical external field is generated between the electrodes which cause changes in the refractive index referred to as the electro-optical effect and, thus, in the propagation speed and in the scatter with the consequence that corresponding changes in the cross-over of light energy also occurs.